The plastic wrapped containers are processed in accordance with the disclosure of copending application Ser. No. 672,228, filed on the same date as this application, both being owned by a common assignee. To control the shrinkage of the heat contractible plastic on the containers (disclosed in the form of glass bottles) at production speed and with esthetically suitable finish on the wraps, which are neither scorched, burned, folded or deformed in the heat shrinking step, a novel method of heating for shrinking the sleeve wrap is needed.
The plastic material used in making the shrinkable sleeves for wrapping the bottle surfaces vary from a foamed polyethylene of high or low density type, a polystyrene foam laminated with a polyolefin or copolymer of olefin (e.g. ethyl ethylene acrylate) in form of a film, a polyethylene foam/polyethylene film laminate or similar types of polyolefins. The plastic wrap material is formed into sheet that is highly oriented in the machine (M) dimension and of as low orientation as is practical in the transverse (T) dimension, such that the ratio of orientation or shrinkage of M/T is 2.0 or more; preferably on the order of 7.0-9.0. Typical orientation shrink values are above 30% shrinkage in the M dimension and preferably 60-80%, and 0-15% shrinkage in the T dimension. The oriented sheet material, laminated or otherwise, is next "flat" printed with a decoration and/or label print using present inks and color materials. The printed stock, trimmed to a web and in rolls, is processed in the machinery through a sleeve former such that the circumference of the formed sleeves is along the M dimension of the oriented plastic web. The sleeves are just slightly larger on their inner circumference than the outer circumference of the largest part of the bottle.
After the sleeve is placed on the bottle, they are carried together into the oven device by a straight line conveyor, and therein the shrinking heat is applied such that it does not deface or damage the printing on the outer facing surface of the sleeve, yet the shrinkage must be performed relatively quickly and in controlled fashion to maintain a good production rate (speed) in a reasonable span of oven and shrinkage of the named materials, which are most difficult to control, must be done so as to provide a smooth and esthetically pleasant appearance in the final wrapped bottle. Marginal control of the shrunken wrap is required to avoid wavy tops or fold over in the sleeve. Satisfactory surface appearance of the final wrap shrunken on the bottle is a requirement.